The long-term objective of the proposed research is to determine the mechanisms of bidirectional transport across the nuclear pore complex. Transport in and out of the nucleus begins with recognition of the transported cargo by a dedicated set of transport receptors. After docking at the nuclear pore, the cargo-receptor complex moves through the pore channel, which is lined with nucleoporins. Loading and unloading of cargoes and interactions of the transported complexes with the nuclear pore are the defining events of nuclear transport. In many cases, the RanGTPase and its regulators controt the direction of movement through the pore. Targeting of large complexes such as the ribosome for export out of the nucleus imposes an even greater complexity on the process of nuclear transport. The Specific Aims are to determine how: 1) ribosomes are exported out of the nucleus;2) nuclear transport factors make contact with the nuclear pore complex;3) the organization of the Ran regulators in the nucleus integrates nuclear transport and gene regulation;and 4) the integrity of the nuclear envelope is maintained. Defects in nuclear localization are associated with a number of diseases thus contributing to the health-relatedness of the project. Nuclear-cytoplasmic transport provides a mode of regulation for gene control in response to, for example, growth cues, stress, viral infection, immune response, and activity of tumor suppressors. The activity of certain proteins can be affected by altering their intraceltular location between the cytoplasm and the nucleus making nuclear transport a potential therapeutic target. In sum, understanding the process of nuclear transport and how it is regulated, may lead to new drug targets and ways to enhance viral-based gene therapies.